Chemical Reaction Engineering (CRE) is the field that studies the rates and mechanisms of

chemical reactions and the design of the reactors in which they take place.

Lecture 12

Lecture 12 – Tuesday 2/19/2013Multiple Reactions

Selectivity and Yield

Series Reactions

Complex Reactions

2

A DkD

A UkU

A B C

A + B C + D

A + C E

Series: A → B → C

Parallel: A → D

A → U

Independent: A → B

C → D

Complex: A + B →C + D

A + C → E

With multiple reactors, either molar flow or number of moles must be used (no conversion!)

3

4 Types of Multiple Reactions

Instantaneous Overall

Selectivity

Yield

There are two types of selectivity and yield: Instantaneous and Overall.

U

DDU r

rS

U

DDU F

FS ~

A

DD r

rY

AA

DD FF

FY

0

~

4

Selectivity and Yield

ABA

BA

U

DUD C

k

k

CCk

CCk

r

rS

2

1

2

21

To maximize the selectivity of D with respect to U run at high concentration of A and use PFR.

DBA 1kBAD CCkr 2

1Example: Desired Product:UBA 2k

BAU CCkr 2Undesired Product:

Selectivity and Yield

5

Gas PhaseMultiple Reactions

6

Multiple Reactions

7

Flow Batch

BB

AA

rdV

dF

rdV

dF

Vrdt

dN

Vrdt

dN

BB

AA

A) Mole Balance of each and every species

Multiple Reactions

8

B) Rates

a) Rate Law for each reaction:

b) Net Rates:

c) Relative Rates:

ACAA

BAAA

CCkr

CCkr

22

11

AAi

iAA rrrr 211

Multiple Reactions

9

C) Stoichiometry

Gas:

Liquid:

T

T

P

P

F

FCC

A

ATA

0

000

0AA FC

Example: A → B → C

(1) A → B k1

(2) B → C k2

Batch Series Reactions

10

1) Mole Balances

Vrdt

dN

Vrdt

dN

Vrdt

dN

CC

BB

AA

AC

AB

AA r

dt

dC r

dt

dC r

dt

dC

V=V0 (constant batch)

Batch Series Reactions

11

2) Rate Laws

B2B1B

A1A

BB1B1

AA1A1

rrr

rr

Ckr

Ckr

Laws

Net rates

1

r

1

r1

r

1

r

C2B2

B1A1

Relative rates

Example: Batch Series Reactions

12

A → B → C

(1) A → B

(2) B → C

1) Mole Balances

CC

BB

AA r

dt

dC r

dt

dC r

dt

dC

ttopt

Ci

AB C

OVV

Example: Batch Series Reactions

13

2) Rate Laws

1

r

1

r

1

r

1

r C2B2B1A1

Relative:

B2B2

A1A1

Ckr

Ckr

Laws:

Example: Batch Series Reactions

14

3) Combine

Species A:

Species B:

A1AA Ckr

dt

dC

tkexpCC 10AA

BB r

dt

dC

B2A1B2B1NET BB CkCkrrrr

tkexpCkCkdt

dC10A1B2

B

Example: Batch Series Reactions

15

Using the integrating factor, tkdtkFI 22 expexp.. tkkCk

dt

tkCd A

B1201

2 expexp

at t = 0, CB=0

BAAC CCCC 0

tktkAC ekek

kk

CC 21 11 12

12

0

Example: CSTR Series Reactions

16

ABCWhat is the optimal ?

00 AAA rCC

0

00 0

BB

BB

rC

VrCv

0

0

000

0

VrvCvC

VrFF

AAA

AAA

1) Mole BalancesA:

B:

Example: CSTR Series Reactions

17

ABC

2) Rate Laws

B2B2

A1A1

Ckr

Ckr

Laws:

1 1

1 2 1 2

0A A A

B A B A B

r r k C

r r r k C k C

Net:

1

r

1

r

1

r

1

r C2B2B1A1

Relative:

Example: CSTR Series Reactions

18

ABC

3) Combine

Example: CSTR Series Reactions

19

ABC

dCBd

0

max 1

k1k2

Find that gives maximum concentration of B

12

01

11 kk

CkC AB

20

End of Lecture 12

21

22

Supplementary Slides

Blood Coagulation

23

24

25

Notations

26

Notations

Mole Balances

27

28

Mole Balances

29

Mole Balances

30

Results

Many metabolic reactions involve a large number of sequential reactions, such as those that occur in the coagulation of blood.

Cut → Blood → Clotting

Figure A. Normal Clot Coagulation of blood(picture courtesy of: Mebs, Venomous and Poisonous Animals, Medpharm, Stugart 2002, Page 305)31

Blood Coagulation

32

Schematic of Blood Coagulation

Cut

A + B

C

D

E

F

Clot33